1. Field of the Invention
The invention relates to an injection syringe which is provided with a cartridge holder and a cartridge. The cartridge holder is a substantially circular cylindrical hollow body which at one end, the rear, is provided with a grip and the other end is provided with projections on its inner surface. The cartridge is also a substantially circular cylindrical hollow body whose outer diameter is slightly smaller than the inner diameter of the cartridge holder so that the cartridge can be accommodated in the holder. At the front the cartridge has an injection needle, and an adjoining constriction or neck. The projections of the cartridge holder engage the neck of the cartridge and thus secure the cartridge in the holder.
2. Description of Prior Art
Injections syringes of this type are known from the Applicant's Netherlands Patent Specification 133,649 or the corresponding British Pat. specification 1,204,709.
In said known constructions the projections consist of cams which are integral with the cylindrical wall of the cartridge holder. The material of the cartridge holder, and thus of the cams, is slightly elastic. Upon insertion of a cartridge, which is provided with a collar and a neck adjoining said collar, into the holder provided with cams, the collar presses the cams slightly outwards so that the collar can pass the cams. After the passage of the collar the cams spring back into the neck portion of the cartridge and thus secure the cartridge in the holder. Such a construction has the drawback that a substantial force is required to obtain the desired radial displacement of the cams, because the applied force must be capable of causing radial expansion of the cylindrical wall of the holder over the circumference of said cylindrical wall at the location of the cams. Practical tests have revealed that automatic insertion of the cartridge into the holder frequently causes breakage of the cartridge. Furthermore, it has been found that after radial displacement the cams in some cases do not entirely spring back into their original position, so that no satisfactory locking is achieved. The dimensions of the cams and the collar must be very accurately adapted to each other, which makes the construction very expensive.
It is also known from U.S. Pat. No. 2,695,613 to provide cartridges with a detachable needle, the needle comprising a grip with resilient arms in which tablike elements are blanked out. This device, however, is not concerned with the problem of non-detachably securing a cartridge in a rigid construction of a cylindrical closed holder.